1. Field of the Invention
The invention relates to printing and detecting markings and, more particularly, to a marking having multi-spectral characteristics.
2. Brief Description of Prior Developments
Mailers and postal services print barcodes on envelopes or labels attached to mail pieces. The barcodes are used to provide information related to processing the mail piece. A POSTNET code, provided by the mailer or consolidator, provides destination address information to the postal service sorters. A PLANET code printed by the mailer is a request to provide simple feedback when a mail piece is processed. Linear barcodes printed on mail pieces must be isolated from each other and from other printed matter on the mail piece. Mail carriers scan bar code labels attached to mail pieces by mailers when they request value-added services such as delivery confirmation. These labels tend to be large and can obscure other information on mail pieces.
Postal services print a mail piece identifier using a lightly colored fluorescent bar code known as a postal-ID tag. The postal-ID tag fluoresces in a broad wavelength band in the orange region and can be excited with broadband ultraviolet light. The fluorescent emission of paper on the mail piece, such as that produced by optical brighteners used in paper manufacturing, and the fluorescence of the postal ID tag, have broad overlapping spectral features, the postal sorter's detection system can be confused. In some cases the fluorescent signal of the ID tags may be diminished by the interfering fluorescence of the optical brighteners.
Postage meters can print indicia with two-dimensional barcodes that provide postage payment evidence. The indicium barcode can include value-added service requests. The provider of that value-added service would have to read every barcode to find the ones that actually request service.
Color barcodes are known, such as the barcode disclosed in U.S. Pat. No. 6,793,138, that increase the information density of printed barcodes. The broad absorption band of the individual colors limits the increase in information density to about three to five times the density of a monochrome code. If several colors are printed in one area, it is difficult to distinguish the different colors. One of the earliest implementation of color barcodes is on small electronic resistors to encode resistance value.
Similar to the use of color, spectral mixtures of fluorescent dyes can increase information density. The dyes have broad emission spectra and a wide range of excitation wavelengths varying from short UV to visible. They also often have a small Stokes shift; i.e., difference between the excitation wavelength and emission wavelength. These properties conspire to make the detection systems more costly and complicated. As in the case of color barcodes, since there are strong overlaps between the emission bands of various fluorescent dyes, the increase in information density is limited. Invisible barcodes are known that can be either luminescent or infrared absorbing. They can be printed over visible information without obscuring the visible information. The known invisible bar codes also have broad spectral features.
All of the symbols and inks described above suffer a common limitation because they are printed with inks that have broad overlapping spectral features. The symbols must, therefore, be printed on different regions of the envelope. Parties participating in the mail stream process suffer the problems of printing symbols without interfering with information that is already there. As an example, consider the POSTNET barcode that identifies the delivery point. A mailer may print an incorrect POSTNET code and deliver the mail piece to a consolidator. The consolidator may print a new barcode, correcting the POSTNET to agree with the address, in the space reserved for higher priority POSTNET codes along the bottom edge of the envelope. The postal service may realize that the recipient has moved and want to print a new POSTNET for the forwarding address. Unfortunately, there is no space assigned for this third POSTNET code. Typically the post follows the inconvenient and obtrusive process of placing a label with the new code over the existing POSTNET code.
“UPU/CEN Mail Communication System Reference Model: General Concepts and Entity Relationship Model”, Draft Version 2.1. Sep. 12, 2005, which is hereby incorporated by reference in its entirety, describes the parties and processes that take part in a mail process. There are multiple applications for communicating via bar codes on the envelopes. The inks used in postal applications typically have broad emission and absorption spectra. The spectra overlap and interfere with each other. Due to the limited area of the envelope the postal service issues regulations that define the required placement of bar codes, clear zones and other information on a mail piece. The resulting mail piece can be cluttered and confusing.
Limited amounts of information can be encoded in the bar codes due to the use of monochromatic inks (black or other colors) and broadband single channel reflectance-based contrast. Readability is dependent on print contrast, which requires high loading of colorant, causing reliability issues for inks. Postal applications need high-density information to enable services, mail piece identification, and postage cryptographic evidencing. Because there is a large number of information fields on the mail piece, there is a strong dependence on registration, printing sequence, and positioning for postal processing of high volumes of mail.
Hand-held scanners lack precise orientation and positioning. Typically each application, on a document having multiple bar codes, uses a separate type of bar code to help with identifying which bar code is for which purpose.
Conventional bar codes are obtrusive, taking a large space on the envelope and making it difficult to see additional information such as ad slogans, addresses, etc. It can be difficult to find a particular bar code and distinguish its signal from the other information.
The limited information capacity of envelopes, and the static nature of information on envelopes gives rise to a need for a database linked to the mail piece information. Maintaining and providing remote access to this database can be expensive, time consuming and technically challenging.
The ease of copying postage indicium barcodes means that it is necessary to detect duplicates based on the information recovered from duplicate mail pieces. Achieving a high duplicate detection rate means that most mail pieces should be scanned and recorded in a duplicates database. The resulting complex infrastructure adds to the cost of the postal process. Previous security inks such as those described in U.S. Patent Application Publication No. 2005/0040234 (Euchner/Auslander) describes printing indicia with ink characteristics such as color and luminescence of mixtures of organic fluorescent dyes. These are all very low-resolution characteristics with overlapping reflectance or luminescence spectra.
Inks with narrow band fluorescence spectra use fluorescent nanoparticle quantum dots or rare earth-doped nanoparticles. Suitable rare earth-doped nanoparticles for incorporating in an ink are described in “Rare earth-doped glass microbarcodes” by Matthew J. Dejneka et al. Evident Technologies manufactures inks for anti-counterfeiting using semi-conducting quantum dots. The use of quantum dots in inks to provide high information density in very small spots has been described in “Information coding and retrieving using fluorescent semiconductor nanocrystals for object identification” by Shoude Chang, et al. in 12 Jan. 2004/Vol. 12, No. 1/OPTICS EXPRESS pg 143. The fluorescent nanoparticle inks described by Barbera-Guillem of BioCrystal, Ltd. in U.S. Pat. Nos. 6,835,326 and 6,576,155 use only the fluorescent characteristics, but not the phosphorescence of the rare earth oxides as additional parameters (for example the decay time). Barbera-Guillem further uses excitation wavelength for the rare earth oxides above 300 nm. The encoded information is limited because they use only monochrome emission wavelength modules in the encoded data without using their combined wavelength in fixed ratio. The comparison of the encoded data to a database such as described in U.S. Patent Application Publication No. 2004/0241424 can be cumbersome and involves handling of a lot of data that is not suitable for a postal application.
Principals participating in the mail generation and distribution process would like to provide information downstream to aid in correct processing of a mail item. There are many such players, and they frequently use bar codes to communicate. Using multiple barcodes results in several problems. The mail item becomes very busy and unattractive. There is confusion in identifying the correct information, so that the postal service must place labels over superceded information. The lack of space on the mail item makes aligning on a clear area difficult. Possible services or corrections are simply not introduced because of the difficulties mentioned.